Core myopathy in two siblings with a biallelic variant in the CACNA1S gene—A case series study

Key Clinical Message Homozygous variants of Calcium Voltage‐Gated Channel Subunit Alpha1 S (CACNA1S) gene mutation were previously identified as causes of periodic paralysis and congenital early‐onset myopathy, while it could be manifested as a late‐onset congenital core myopathy. Abstract Calcium Voltage‐Gated Channel Subunit Alpha1 S (CACNA1S) gene mutation has been linked to various neuromuscular conditions in recent years. Congenital myopathy with core‐like features is one of the cardinal associations reported previously, causing severe respiratory insufficiency and death in neonates. Informed consent was received from the patients. Subsequently, peripheral blood leukocytes were utilized to extract genomic DNA. Moreover, exome enrichment was implemented through the Twist Human Core Exome Kit (Twist Bioscience) and exome sequenced using Illumina NovaSeq 6000 platform (Illumina, San Diego, CA, USA). Sanger sequencing using BIG Dye Terminators confirmed the presence of the final variant. Finally, the candidate variants were classified based on the American College of Medical Genetics and Genomics (ACMG) guidelines. In this report, we describe two siblings, who presented with childhood and late‐onset progressive muscle weakness, and had a homozygous variant in exon 2 of the CACNA1S gene defined as c.188C > A (p.Ala63Asp) (NM_000069.3). The SIFT, Polyphen2, CADD PHRED, and Mutation Taster analysis tools classified the variant as pathogenic/damaging. The muscle biopsy of the younger brother revealed intermyofibrillar network pattern disruption as cytoplasmic core‐like lesions. The muscle magnetic resonance imaging (MRI) reported grade IIa and IIb fatty changes. Finally, the electromyography (EMG) findings suggested a myopathic change pattern. This report illustrates the clinical variability in CACNA1S‐related myopathy by reviewing prior reports and adding newly found aspects, additionally expanding the gene defects associated with core myopathy.